Replacing power transformer on Baby Will

[dimitrip]

Hi,

I have a Epiphone Valve Junior converted to Baby Will, built with the default VJ power transformer which I want to replace with one made by Danbury UK (this one: https://www.ampmaker.com/shop/0-190-275 ... ansformer/). I would appreciate any help you can give me.

Is this a center tap transformer?
Should I remove rectifier bridge diodes 3 and 4?
Do I connect the heater CT pin anywhere on the board? Where?
Anything else I should be aware of?

Thanks in advance!
D.

[geoff 1965]

the transformer is a single winding secondary HT with lower voltage tap so you need to bridge rectify it,it will help if you post a schematic/layout of your amp.

[dimitrip]

Thanks! OK, here is the schematic. I asked because I came across this post which warns about changing the rectifier diode layout when replacing the power transformer.

[geoff 1965]

if yours has the stock valve junior transformer you can swap it in no problem,the heater supply has an artificial centre tap "2 100 ohm resistors" so you can remove those and ground the centre tap of the danbury.add some pics of the amp if you can showing transformer,board etc.
the danbury are good transformers,if you can fit a on/on switch you can use the second tap to drop to half power if you wanted.

[dimitrip]

So, I don't need to remove diode rectifiers 3 and 4 if I ground the transformer CT? And where on the board do I connect the CT?

Photos:

[TriodeLuvr]

So, I don't need to remove diode rectifiers 3 and 4 if I ground the transformer CT? And where on the board do I connect the CT?

Photos:

Yes, you need to remove D3 and D4. Connect the centertap as close as possible to the negative end of C13/R1.

Jack

[geoff 1965]

the HT has no centre tap! you need to keep the 4 diodes "bridge rectifier" for the danbury transformer.my laptop won't open those pics for some reason.

[JMPGuitars]

Hi,

I have a Epiphone Valve Junior converted to Baby Will, built with the default VJ power transformer which I want to replace with one made by Danbury UK (this one: https://www.ampmaker.com/shop/0-190-275 ... ansformer/). I would appreciate any help you can give me.

Is this a center tap transformer?
Should I remove rectifier bridge diodes 3 and 4?
Do I connect the heater CT pin anywhere on the board? Where?
Anything else I should be aware of?

Thanks in advance!
D.

There's confusion in this thread. I'll clear it up. Having a center tap doesn't mean anything, unless you understand where the center tap is. Sometimes both the heaters and HT have center taps. Sometimes only one does, sometimes neither do.

The only thing that matters is what YOUR transformer has.

Your transformer has a center tapped heater. That means you remove the 2 100 ohm resistors that were creating an artificial center tap for the heaters. Then you connect the new heater center tap to the chassis star ground.

Your HT (labeled Sec 1) is NOT center tapped. It has options for the voltages, but no center tap. Do not remove any diodes. Only 2 wires should be connected to the HT, no 3rd CT wire.

Thanks,
Josh

[dimitrip]

Thanks! I did the swap, kept the diodes intact and only removed the two 100K resistors (left of J1).

It worked! The breakup sounds significantly better, creamier and dies smoother.

However, I noticed some noise at high volume which wasn't there before. There is hum noise and there are three resonant high-frequency peaks. The 10kHz one only appears when Volume and Tone both exceed 75% or so. The two higher ones are there constantly and relative to both Volume and Tone. I captured the output through a load box.

noise-resonances.png

Any idea what may have caused this?

Cheers,
D.

[JMPGuitars]

Any idea what may have caused this?

Post clear photos of the inside of your build. To me it sounds like a grounding issue, but we need to see more.

[dimitrip]

Thanks for taking the time to help, I will take some photos tonight.

By the way, forgot to mention that the amp is dead quiet unplugged.

[JMPGuitars]

By the way, forgot to mention that the amp is dead quiet unplugged.

They usually are.

[dimitrip]

Not sure what angle is best, but I took a few photos. Here's the first bunch...

[dimitrip]

And here's the second one.

[JMPGuitars]

There is a LOT going on there. The first thing is that your transformer mounting and orientation is a little scary.

At the very least, you need to get better mounting bolts, and lock washers, and make sure the transformer is firmly mounted. Transformer vibration alone could cause hum.

There's also a lot of issues on the build, like suspect solder joints, and excess flux that needs to be cleaned up.

[crgfrench]

R8 ain’t 56k

[dimitrip]

Thanks guys!

I know the job is sloppy, I'm new to this and want to learn. I'll try to clean it up. However, before swapping the PT I had none of these noise and resonance issues and the amp was very quiet.

The R8 was bridged according to the tweaker's table on the schematic, in order to add a little more gain (R24 switched from 56k to 100k as well).

[JMPGuitars]

I know the job is sloppy, I'm new to this and want to learn. I'll try to clean it up. However, before swapping the PT I had none of these noise and resonance issues and the amp was very quiet.

This is why I suggested improving the transformer mounting first. Transformer vibration can cause noise. It needs to be mounted better. You might want to add some fender washers to the chassis to stiffen it up for the transformer.

[dimitrip]

I'll do that first, cheers!

[Bieworm]

I know the job is sloppy, I'm new to this and want to learn. I'll try to clean it up. However, before swapping the PT I had none of these noise and resonance issues and the amp was very quiet.

This is why I suggested improving the transformer mounting first. Transformer vibration can cause noise. It needs to be mounted better. You might want to add some fender washers to the chassis to stiffen it up for the transformer.

You mean f*nder washers